This project seeks to achieve an improved understanding of the structure and function of the cytoplasmic ground substance (CGS). Thus far the investigation has defined the existence of a structured matrix in which the formed elements of the cytoplasm such as cisternae of the endoplasmic reticulum, the microtubules and polysomes are suspended. Examined in whole cells with the high voltage electron microscope, the cytoplasmic matrix (or CGS) comprise a three-dimensional lattice of slender strands or microtrabeculae and intertrabecular spaces. The latter are structure- and material-free and are regarded as representing the water-rich phase of the cytoplasm. The trabeculae, on the other hand, are interpreted as the protein-rich phase. In studies so far we have examined the responsiveness of the lattice to variations in divalent cation concentration, to temperature changes and to tonicity of the extracellular environment. The response in each instance is both dramatic and unique to the condition studied. In the period of the grant for which the continuing support is requested, we expect to finish the above studies and prepare them for publication. In addition, we expect to initiate studies that will characterize the residue of the lattice after extraction with non-ionic detergents. So far, this has shown the lattice to be rich in actin filaments and intermediate filaments. These are structurally contained in the lattice and simply exposed by the detergent wash. We also expect to follow the morphogenesis of myofibrils in cultured heart myoblasts toward the end of understanding the phenomena of differentiation. Thus far, it is evident that the lattice of the CGS takes on a special form in association with fibrillogenesis and that the organization of the fibril is anticipated in the organization of the lattice. The f-actin and myosin seem to form within the strands of the lattice and in association with non-randonly distributed polysomes. We propose, in addition, to use antibodies labeled with colloidal gold to identify in the electron microscope image the distribution of the newly-formed actin and myosin filaments. Finally, we are planning to examine in the near future the effects of ultraviolet microbeams (270nm) on the form and function of the lattice in the transport of pigment granules in chromatophores.